twin + adoption studies (rm)

• twin studies AO1


  . twins ae compared to see if behaviour is genetically or environmentally based

  . psychologists compare behaviour between groups of monozygotic twins and dizygotic twins using concordance rates or correlation

  . assumption that both tin types grew up in same environment so only difference is how genetically related they are

  . if behaviour is entirely genetic we expect MZ twins to have 100% concordance rate

  EXAMPLE: Gottesman and shields - investigated genetic basis of schizophrenia - 57 twin pairs used (opportunity sample), found if one MZ twin had schizophrenia the other would be 42x more likely to have it than someone in general pop and if one DZ twin had it the other same sex twin would be 9x more likely
• twin studies AO3 strengths

  . enables researchers to investigate the influence of genes due to assumption of shared environment

  . information for twin studies usually taken from twin registries which hold data on thousands of twins - sample is large and data likely to be representative
• twin studies AO3 weaknesses

  . may overestimate genetic influence - MZ twins more likely to share a more similar environment than DZ twins so some similarity may be due to environment

  . provide broad indication that a behaviour has genetic origin but can't identify the specific genes involved - more technology required to uncover the specific genetic influence
• adoption studies AO1


  . adopted children are compared with their biological relative and adoptive relative - if more similar to biological the behaviour is likely more genetic, of more similar to adoptive then behaviour is likely more environmental

  EXAMPLE: Heston - aimed to see how many adopted children of biological mothers with schizophrenia would also develop it, took 47 adults adopted at birth with schizophrenic mothers and 47 with mentally healthy mothers, were assessed to see for development of it, found 10% of adopted had developed it - matched data which showed risk of developing it if one parent had it was 10% - concluded findings support influence of genes in schizophrenia
• adoption studies AO3 strengths

  . have advantage of removing the extraneous variable of environment

  . useful in showing that twin studies may overestimate genetic factors
• adoption studies AO3 weaknesses

  . children may be adopted into families similar to their biological ones = environmental influences similar = apparent similarities with biological relatives may just be due to environmental similarities

  . people who adopt may not be representative of population = conclusions drawn about the effect of genes eg intelligence may not generalise to population as a whole